The Blueprint. To understand any green coffee process, it’s helpful to remember a coffee bean is the seed of a coffee cherry. When cherries are harvested, it is the job of the farmer or local processor to remove everything surrounding the seed before it gets shipped to us/you for roasting. The layers relevant for processing are the skin/pulp (exocarp), the fruity layer of mucilage (mesocarp), and the thin, paper layer (endocarp), referred to as parchment (for obvious reasons).
Beneath the parchment is another very thin papery layer called silver skin, which you will see evidence of around green beans before roasting and also jammed into the center cut of the bean during and after roast. This is the chaff that blows around your garage or shop while roasting.
Every type of process requires the removal of these layers and the ultimate drying of the beans to around 10% - 12% moisture content before being bagged and shipped. These steps are riddled with risks at various stages and will influence the final cup.
Washed coffees, as you might expect, employ the use of (LOTS of) water. Here are the basic steps:
Sorting. First, the cherries are sorted after harvest, aiming to mitigate any defective fruit. This is done partly by hand and partly by floating them through tanks of water. Under-ripe fruit are inclined to float while their ripe counterparts (fully formed, dense coffee seeds) will sink.
Pulping. As the name implies, a mechanical process is used to break the skin and pulp of the fruit, leaving a slimy tank of seeds behind. These are floated through large tanks of water and, again, defective beans that are poorly formed will float and be sorted out of the batch. (If you’ve ever seen a piece of wood with dry rot, you’ll know how much lighter it is).
Fermentation. The remaining seeds will be left to soak in water for around 18 – 24 hours, creating an environment for microorganisms to go to work, breaking down the slimy mucilage that remains on the bean. As you can imagine, this is a delicate step and can have a dramatic impact on the ultimate flavor profile. The amount of time will vary based on factors such as ambient temperature, water temperature, or regional preferences.
Drying. The final stage is drying the coffee to a target moisture content as noted above. This can be done on drying beds under the sun, requiring regular raking and mixing to prevent mold from developing. It can also be done in mechanical dryers, which can manage the drying process much more precisely. Often, a combination is used (sun drying beds for a couple days, followed by mechanical dryers) to save energy costs.
Once fully dried, the coffee is now in what is referred to as its “parchment” stage or, simply, “parchment coffee,” meaning that it still retains that last, crisp layer. Parchment beans sound and feel different than green coffee before roasting—like unshelled pistachios?
Taste. In many respects, washed coffees most accurately celebrate the flavor of the bean itself. Because the rapid, aggressive washing with water removes the fruit so completely, none of that fruit is given time to affect the coffee’s flavor. The trait often touted in washed coffees is, “clean” or “bright.” This is a result of lively acidity—something that can become dampened by other processes. Better consistency is also typical of washed coffees because so many processing variables used in other methods have been skipped.
In the end, washed coffees tend to portray a bean's origin exceptionally well. In such an unmasked state, you’ll be able to taste the delicate differences among cultivars and regional distinctions. Some remarkable examples are the many Kenya’s that are “double fermented” for an even cleaner cup!